According to EPA’s Guidelines for Exposure Assessment (U.S. EPA, 1992), direct measurement or point-of-contact exposure measurement "evaluates an exposure as it occurs, by using direct methods to measure the chemical concentrations at the interface between the person and the environment as a function of time, resulting in an exposure profile." Point-of-contact exposure measurements are performed using personal monitoring techniques (i.e., personal air sampling or diet sampling) that record an individual’s direct exposures during a specified time period. Provided measurement techniques are available and accurate, this method is likely to produce the least uncertainty in estimating exposure concentration, at least over the time period of the measurements. Point-of-contact measurement, however, can be cost-prohibitive and can require extrapolation from short-term sampling to long-term exposure, thereby increasing uncertainty. Additionally, direct measurement of exposure is neither source-specific nor representative of an entire population. Direct exposure measurements could be used to validate or verify results of assessments conducted using indirect estimation, such as scenario or population-based evaluations (U.S. EPA, 1992).

Observational human exposure studies require strict adherence to ethical guidelines. From problem formulation to study implementation, careful considerations must be taken at each step to ensure the health and safety of human subjects. Specific actions will vary depending on the type of research being conducted and characteristics of the human subjects. Based on proceedings from an expert panel workshop, NERL produced The Scientific and Ethical Approaches for Observational Exposure Studies (SEAOES)(133 pp, 1.2MB, About PDF) (U.S. EPA, 2008), providing detailed information on regulatory requirements and ethical and moral issues associated with the protection of human subjects.